Use of the method of moments for analysis of antennas composed of conducting wires and plates

When the characteristics of antennas with a junction of conducting wires and plates, such as antennas used for portable telephones, are analyzed by the method of moments, a special segment having a wire current and a radial surface current has been used. However, the radius of the radial current of this segment is required to be greater than about 0.2 wavelengths to obtain accurate numerical results. Therefore, this method cannot be applied to antennas having conducting plates whose dimension is less than 0.2 wavelengths. In this paper, another special segment, the "joint patch segment," which connects the radial segment with the planar segment, is proposed to overcome the limitations of the radial segment. In order to demonstrate the accuracy and the advantages of the proposed method, the frequency characteristics of the input impedance of the planar inverted F antenna mounted on a conducting box are calculated and compared with experimental data.